Question

cum se face a)
va rog!! 

Answer 1

$C_x^{y} = C_x^{y+2} \\ C_x^{2}=153 \\ Din\,ecuatia\,a\,2-a\,\,il\,calculam\,pe\,\,x \\ \frac{x(x-1)}{1*2}=153 \\ x(x-1) = 2*153 \\x(x-1) = 306 \\ x^{2}-x-306=0 \\ x_1 = \frac{1+ \sqrt{1+4*306} }{2} = \frac{1+ \sqrt{1225} }{2}=\frac{1+ 35 }{2} = \frac{ 36 }{2} = 18 \\ x_2 < 0\,\,se\,elimina \\ Din\, prima\, ecuatie\, rezulta: \\ y + (y + 2)=x \\ y + y + 2 = 18 \\ 2y=18-2 \\ y= \frac{16}{2} = 8 \\ Avem \, solutia: \\ x=18 \\ y=8$